This invention relates to an electric key operated by electric signals, and more particularly, to an electric key which can be operated with a small amount of electric power.
In a conventional electric key operated by electric signals, a locking and unlocking motion is carried out by a solenoid or a motor. However, in order to operate the solenoid or the motor, electric power of several watts usually or several tens of watts must be conducted for over 100 msec. That isf electric power of more than 1 joule is consumed when the door is locked and unlocked.
Therefore, when a dry battery is used as a power source, service life span of the dry battery is very short even if the dry battery has a large capacity, thereby requiring exchange of dry batteries within a short time of one year or less than one year.
This type of electric keys is disclosed in Japanese Patent Laid Open Publication No. 38800/1974 and Japanese Patent Publication No. 45278/1976. An electric key disclosed in Japanese Patent Laid Open Publication No. 38800/1974 has an electromagnetic means which accomodates a permanent magnet for keeping a movable magnetic core at locked and unlocked positions. That is, conduction in the electromagnetic means is not necessary for maintaining the movable magnetic core at two respective locked and unlocked positions. However, the electromagnetic means must be energized or conducted to move the movable magnetic core from the locked position to the unlocked position and vice versa while distinguishing the magnetic flux of the permanent magnet.
Further, Japanese Patent Publication No. 45278/1976 also discloses an electromagnetic means having an armature to be operated by an electromagnet. Also in this case, the electromagnetic means must be energized to decrease or cancel the magnetic flux of a permanent magnet in both cases where the key is locked and unlocked. In these electromagnetic means, the movable magnetic core and the armature are moved through a space of 2 to 4 mm, respectively. This motion needs a big amount of electric power because the ampere-turn for obtaining magnetic flux necessary for a space is in proportion to the length of the space and the electric power is in proportion to the square of the ampere-turn.
Accordingly, as these disclosed electric keys require a big amount of electric power, the life span of dry batteries used for these keys is very short.